Concatenate a String and Integer in Python

String manipulation is a common task in many languages, especially when creating user interfaces. One of the most common tasks is to concatenate a string and an integer together. Here we'll show you a few different ways to achieve this in Python.

Adding a String and an Integer

Using the + operator, we can add a string and an integer together. However, you must first convert the integer to a string since Python won't do it for you.

>>> the_str = "My daughter's age is: "
>>> age = 3
>>> the_str + str(age)
"My daughter's age is: 3"

If you don't convert the integer to a string, you'll get an error similar to this:

>>> the_str = "My daughter's age is: "
>>> age = 3
>>> the_str + age
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: cannot concatenate 'str' and 'int' objects

f-Strings

Another option that works well for formatting strings is Python 3's "f-string". This is a new feature in Python 3.6 and allows you to format strings in a more readable way.

>>> the_str = "My daughter's age is:"
>>> age = 3
>>> f'{the_str} {age}'
"My daughter's age is: 3"

While this isn't necessarily a shorter way to achieve the same thing (it takes 18 characters vs 17 with the + operator), it is a much more readable way to format strings.

One thing that's nice about doing it this way is that some of the formatting can be done in the f-string and not in the string variable. Notice that the_str doesn't have a space at the end, which is now in between the variables in the f-string.

Format

Finally, there is a third option for formatting strings. You can use the format function to format strings, which uses placeholders within strings.

>>> the_str = "My daughter's age is:"
>>> age = 3
>>> '{} {}'.format(the_str, age)
"My daughter's age is: 3"

This is slightly similar to f-strings, but it is a little more verbose and available in Python 2.x. And again, it has the advantage of allowing more formatting to be put in the placeholder string and not the variables.